Advancements in the design of Organic Light Emitting Diode (OLEDs) displays, such as Active Matrix OLED (AMOLED) displays, have resulted in an increase in the variety of applications that incorporate such display technology. Unlike many other types of conventional backlit LCD designs, AMOLED devices include light emitters in each individual pixel and require no backlight. These individual pixels emit light with intensity proportional to the electrical current supplied to the in-pixel OLED device. This OLED current (IOLED) is controlled by circuits associated with each pixel, which may include one or more thin film transistor. (TFT).
AMOLED displays inherently degrade upon prolonged usage. AMOLED displays typically contain in-pixel circuit algorithms to compensate for transistor and OLED material degradation. These in-pixel algorithms are optimized for panel performance (luminance, spatial uniformity, etc) and reliability. However, the limits of compensation provided by these in-pixel circuit algorithms can be reached after prolonged and continuous usage. Once these limits are reached, the optical performance of the display reduces and is able to cause the panel to be un-usable or to at least fail out of specification.
The TFT devices generally implement an algorithm that is applied to externally supplied image data to supply the OLED element with an IOLED that results in the desired grayscale level for that pixel. The TFT configuration that applies this algorithm is referred to as an “in-pixel compensation circuit.” The performance of the TFT components of a display commonly exhibit variations over time, variations relative to different locations across the display, or both. Degradation of OLED device elements themselves includes decreases over time of both turn on voltage (VF) and quantum efficiency (QE). The effect of the combination of the degradation of the TFT components and OLED components results in both a temporal and a spatial degradation in optical performance for the display. This composite degradation is referred to as “OLED panel aging”. OLED panel aging results in optical luminance degradation that is spatially, temporally, and content dependent.
Therefore, the long term usability and performance of a display is able to be improved by an efficient technique that spatially monitors, i.e., across the pixels of a display, the actual performance degradation of a display over time to produce display aging compensation coefficients that are used to compensate grayscale data supplied to each pixel of the display.